This invention relates to improvements in heat fusing apparatus and more particularly to heat fusing apparatus in which a heated roll is brought into contact with an image formed of a resinous powder to heat the powder and fix the powder image to a sheet of paper.
Contact fusing apparatus is known in the prior art. However, contact fusing has the disadvantage that "offset" may occur. Offset is caused by part of the image sticking to the surface of the contact fusing device so that when the next sheet comes into contact with the fusing device the image partially removed from the first sheet is transferred to the second sheet. This offset problem has been overcome in commercial machines by fabricating the outer surface of the heated roll with a resilient material such as silicone rubber which, when operated with a deformable backup roll, will produce offset-free operation without the use of any offset-preventing liquid such as silicone oil. This fusing roll has had sufficient useful life so that it is suitable for use in a system which utilizes high process speeds in which the components of the system are required to have maintenance free operation for a long period of time. However, in actual service, there is a condition where the surface of the heated roll collects toner and paper particles or dust over a period of operating time which results in thoroughly contaminating the heated roll's silicone rubber surface with toner. This condition, which has been known as a "toner ring," causes machine malfunctions in the form of a loss of information on the printed sheet, causes paper to stick to and wrap around the hot roll and can cause data insertion on the printed page.